1. Field
This invention is generally related to oscillators, and more particularly, to configurable wide tuning range oscillators.
2. Background
Oscillators may be used in a variety of communication systems, including radio frequency (RF) systems and other wireless communication systems. Within the variety of communication systems, oscillators may be used in transmitter and receiver circuits. Two common types of oscillators are the voltage controlled oscillator (VCO) and the digital controlled oscillator (DCO).
Evolving technologies and industry standards related to wireless communication systems have led to a need for more flexible and efficient oscillators. The standards lead to varying requirements for phase noise and oscillator amplitude. A highly configurable oscillator is desired to optimize performance of wireless communication systems operated pursuant to the standards. Efficiency considerations include minimizing oscillator current consumption in order to increase talk time, and the flexibility to cover multiple frequency bands.
Past attempts at such configurable oscillators include: (a) providing multiple oscillators wherein each oscillator covers a small portion of the overall frequency range, and wherein each oscillator is optimized for a certain standard in terms of power and phase noise; (b) providing a single oscillator combined with multiple divisions and mixing to generate an array of frequencies; (c) providing transformer based oscillators, for example, as discussed in U.S. Pat. No. 7,423,495, issued to Bevilacqua, et al., on Sep. 9, 2008 and titled, “Oscillator and Method for Generating an Oscillator Signal,” which is entirely incorporated by reference herein; and (d) providing multiple active cores of varying size switched in and out of one LC tank to cover a wide tuning range, as discussed by D. Hauspie, et al., in “Wideband VCO with simultaneous switching of frequency band, active core and varactor size,” IEEE J. of Solid State Circuits, vol. 42, no. 7, Jul. 2007, which is entirely incorporated by reference herein.
Providing multiple oscillators wherein each oscillator covers a small portion of the overall frequency range may require a large area devoted to the oscillator system due to the use of numerous inductors. For example, at least one inductor may be required for each oscillator.
Providing a single oscillator combined with multiple divisions and mixing to generate an array of frequencies may result in excessive power consumption and a reduction in programming flexibility in terms of power and phase noise. In addition, there may be undesired spurs due to the multiple stages of mixing.
Providing transformer based oscillators may require a transformer with a large magnetic coupling (k factor) which may be difficult to realize, and on chip implementations generally result in a lower Q.
Providing multiple active cores of varying size switched in and out of one LC tank to cover a wide tuning range may result in an increase in current consumption at the lower end of the frequency tuning range as further components are switched in.
While various techniques have been attempted for more efficiently meeting varying requirements for phase noise and oscillator amplitude, the known techniques do not provide an optimum solution for a configurable wide tuning range oscillator and may include undesirable limitations. A need exists for better techniques for more efficiently meeting varying requirements for phase noise and oscillator amplitude in wireless communication systems.